Chronic hepatitis B genotype E in African migrants: response to nucleos(t)ide treatment in real clinical practice

Hepatitis B virus (HBV) chronic infection is a very prevalent disease worldwide. It is estimated that more than 240 million people are infected and that around 686,000 people annually die from complications of this disease, including liver cirrhosis and hepatocarcinoma [1].The vast majority of them live in low- and middle-income regions such as sub-Saharan Africa, where roughly more than 50 million people are infected.

Hepatitis B could be considered, in some parts of the world, a neglected disease for a number of reasons [2]:the major burden of morbidity and mortality from HBV is borne by tropical and subtropical countries; HBV infection is a silent disease leading to a large pool of undiagnosed infection; it disproportionately affects populations living in poverty; it causes stigma and discrimination; lack of public/media representation because HBV is “eclipsed” by higher profile infections such as HIV or malaria; lack of existing investment and development of infrastructure through which to provide education, prevention, diagnosis, and treatment; poor-quality data contributing to misinformation about epidemiology and risk factors and lack of assessment regarding feasibility of interventions; and, finally, lack of major dedicated funding agencies. As a result, mortality due to viral hepatitis (HBV and HCV) is increasing while mortality from other diseases such as HIV and malaria has declined [3].

To date, 10 genotypes (A-J) and more than 40 sub-genotypes have been identified for HBV. The distribution of HBV genotypes differs throughout the world [4]: genotypes A and D are the most prevalent in Europe; D in Asia; B, D and G in North America; F in South America; and E in sub-Saharan Africa, comprising up to 70% of all African HBV-infected patients.

HBV genotype may influence disease progression and antiviral response [5] and there are numerous studies related to such aspects: evolution of the disease according to genotype or risk of chronicity [6‐9]; percentage of HBeAg or HBsAg loss [10, 11]; HBV DNA levels [12‐15]; risk of progression of liver disease [16, 17] and risk of hepatocellular carcinoma [18‐20]; and response to treatment [21‐25]. However, most studies are performed on genotypes A, B, C, and D.

Although it seems to harbour intrinsic potential oncogenic activity and virological characteristics of immune scape [26], there is limited literature on the natural course of HBV genotype E chronic infection, and even fewer studies addressing its response to antiviral treatment.

A search in PUBMED with the commands “hepatitis B” AND “genotype E”, without any type of filter, retrieved 141 articles. Of these, only 10 [12, 27‐35] (7.1%) describe genotype E response to treatment in a variety of distinct scenarios: HIV-HBV co-infected patients [27‐30], rescue after lamivudine failure [31], adefovir phase III clinical trials including a total of 6 genotype E patients [12]; response to interferon [33, 34] and a follow-up study of HBsAg decline in entecavir-responding patients [32]. Finally, one retrospective study addresses HBV genotypes E-H response to antiviral therapy in naïve mono-infected patients but includes just 6 genotype E patients treated with nucleos(t)ide analogues [35]. Current international guidelines do not consider either patients with HBV-genotype E chronic hepatitis [36].

HBV genotype E almost exclusively occurs in African people but due to the significant migratory flow from sub-Saharan countries that has occurred in Europe in recent years, an increasing number of patients with chronic HBV hepatitis are been treated and followed up [37]. In some studies, more than 80% of these patients had a genotype E [38]. A better knowledge of the evolution of CHB genotype E infection and its response to treatment is of great importance when making recommendations that could differ from those issued for other genotypes, in order to deliver proper medical care.

Our Tropical Medicine Unit (TMU) belongs to the Hospital of Poniente, sited in the province of Almeria, in Southern Spain. It serves a population of about 270,000 people, of which around 30% are immigrants, with a high proportion of people coming from West African countries. Chronic hepatitis B is one of the most prevalent infectious diseases among immigrant patients, especially among those of sub-Saharan origin [39].

The aim of this study is to analyze the response to treatment with NA (entecavir or tenofovir) in sub-Saharan patients with CHB genotype E infection in real world practice.

During the study period, a total of 2209 sub-Saharan patients were assisted at the TMU; 609 (27.6%) of them presented CHB infection: 370 (60.7%) were classified as inactive chronic carriers, 181 (29.7%) were in a chronic HBeAg-negative phase, and 58 (9.5%) in a chronic HBeAg-positive phase. Treatment was initiated in 72 patients; genotype information was available in 55 of them: 43 (84.3%) genotype E, 6 genotype A, and 2 genotype D. Finally, out of the 43 patients with genotype E, 15 were excluded because they did not meet the inclusion criteria of the study. Thus, a total of 28 patients were included.

With the data we provide, we can state that treatment with nucleos(t)ide analogues in sub-Saharan patients with CHB genotype E infection have at least as favorable results as the ones reported for other genotypes, in terms of virological response rates, normalization of transaminases, and loss of HBeAg.

These finding are relevant because sub-Saharan people are one of the populations with the highest prevalence of HBV infection of the world, and genotype E in particular is highly endemic in most of sub-Saharan Africa. Even though HBV genotype E horizontal transmission is also possible, among the migrant population coming from sub-Saharan Africa the infection is most frequently acquired vertically at birth or during the first years of life as a consequence of traditional medicine practices and tribal scarifications [44]. This fact means that, although our patients were fairly young (mean age 31.5 years), HBV infection has probably been present for all that long.

There are many studies relating to chronic hepatitis B infection in recent years but a paucity of information is available on the clinical and virological characteristics of HBV genotype E-infected patients as well as on the efficacy of anti-HBV drugs. Epidemiological studies have suggested the carcinogenic potential of genotype E, and in fact, African regions in which genotype E is endemic are characterized by a higher incidence of hepatocellular carcinoma. Although the mechanisms underlying this hypothetic oncogenic potential have not yet been clarified, they could be related to immune escape phenomena [26] as well as to other possible variables involved, such as HIV co-infection, dietary iron overload or aflatoxins consumption [45].

As there is a growing migration movement from these African regions to western countries [46], dealing with migrant patients with hepatitis B genotype E is becoming more frequent in western hepatology clinics and hospitals. Out of the actual clinical practice studies, only the studies by Marcellin [47] et al. and Boglione et al. [32, 34] include a considerable number of sub-Saharan patients, although in Marcellin’s study no genotype information is available.

HBV genotype may influence antiviral response, but the main studies that analyze the role of HBV genotype in the treatment with NA mostly deal with genotypes A, B, C and D [5, 48]. The importance of our work is that, to our knowledge, is the first prospective clinical practice study truly exploring the virological response to NA therapy in CHB genotype E patients.

There is one clinical practice study about treatment of CHB genotype E patients with NA [32], but it is focused in the decrease of HBsAg titles. In this work, the authors conclude that the decrease of HBsAg titles is smaller in the 34 patients infected by genotype E as compared to patients infected by genotypes A or D, although the analysis only included those patients who had achieved previously virological response (HBV-DNA undetectable after 24 weeks of therapy), and the meaning of HBsAg-title changes in this setting is still unclear. Another study with genotype E-infected patients, also conducted by Boglione et al. [34], explores the response to interferon therapy finding very low rates of response; 10 patients were rescued with entecavir after failing interferon treatment and virological response was achieved in 60% of them after a follow-up median of 5.2 months. There is also one retrospective study that addresses HBV genotypes E-H response to antiviral therapy in naïve mono-infected patients, but includes just 6 genotype E patients treated with nucleos(t)ide analogues [35]. Current international guidelines do not yet mention patients with HBV-genotype E chronic hepatitis [36].

Finally, a handful of articles deal with CHB genotype E patients and NA treatment in different clinical scenarios, like HIV-HBV co-infected patients [27‐30], rescue after lamivudine failure [31], and the phase III studies of adefovir dipivoxil reported by Westland et al. [12] where 6 patients with genotype E were included.

In our study we have included 28 treatment-naive patients and have observed that at 12 months of treatment with NA, 89.4% of HBeAg-negative and 80% of HBeAg-positive patients negativize the viral load. This proportion increases to 100% in both groups at month 18. In other studies conducted in real clinical practice with chronic hepatitis B patients, overall viral load negativization rates at 12 months in patients treated with tenofovir ranged from 59.2 to 91.9% [24, 25, 47, 49‐51]; and with entecavir, from 41 to 89.4% [21‐23, 51‐62]. These differences between the studies are possibly due to the diverse populations studied in each case, the different sensitivity of the PCR used to detect viral load, and to the fact that, in many studies, patients previously treated with other treatments for HBV are included. None of these studies do, however, mention HBV genotyping.

Table 2 compares those other studies that do analyze the response to treatment, as ALT normalization and viral load undetectability, according to HBV genotype. Among the few available studies, it stands out one conducted by Ono et al. [22], where genotype C predominates (70.9%), and the proportion of patients with undetectable viral load after one year of treatment is 88%, similar to that of our work. In the study of Zoutendijk [23], where genotype D predominates in non-cirrhotic patients (49%), 68% of patients have undetectable viral load after one year. Due to the relatively small number of patients included in these studies, no clear conclusions can be drawn about a faster response to treatment in patients with one genotype or another. Although these data may suggest that patients with genotypes C and E respond faster to treatment with nucleos(t)ide analogues than those with genotype D.

Regarding normalization of transaminase levels, in the present study rates were 42.1 and 85.7% after one year in HBeAg–negative and HBeAg-positive patients respectively. These percentages reached 55.6% in HBeAg-negative and 100% in HBeAg-positive patients at 18 months of follow up. In other studies of actual clinical practice, the percentage of patients with normal transaminases at 12 months ranged from 34.6–95.5% [21‐25, 47, 49‐53, 56‐60, 62]. These discrepant results may be explained by the different cutoff points taken for normal ALT in the different studies, and by the different stages of hepatopathy of the included patients, since in some cases they include patients with established cirrhosis and even with hepatocarcinoma.

HBeAg loss occurred in 85.7% of patients in a median time of 31.8 months. Seroconversion rate during the first year was 12.5%. Although there are few HBeAg-positive patients in our study, these results are similar to those found in other published works where these rates oscillate between 8 and 16% [22, 24, 53, 55, 61].These studies also show that HBeAg-loss rates increase significantly after more than 3 years of treatment. In these works, like in ours, no HBsAg loss is observed.

It should be noted the high adherence to treatment observed in our study: 86.7% in the first year and almost 100% in the second year. Among migrants this may be especially striking, since many are the reasons that hamper their compliance and follow-up (labour mobility, visits to their home countries, barriers to access to health care systems, etc.). The reasons for such good adherence are probably related to the collaboration of mediators and community health agents, the use of cost-free drugs, and the lack of barriers to access to the public health care system, either primary or specialized care, as is established in Andalusia, our administrative region.

The main limitation of this study is that the number of patients is not very high, although figures are according to the scarce published studies that describe the response to treatment of genotype E chronic hepatitis B patients, either with interferon or with nucleos(t)ide analogues [12, 32, 34, 35]. It would have also been interesting to compare patients with genotype E with other patients of similar origin and socioeconomic circumstances but with different genotypes. In relation to this last aspect, the number of African migrants that we deal with harbouring other genotypes is so low that does not allow valid comparisons. One last limitation is that therapeutic drug monitoring and HBsAg quantification were not available in our hospital, even though the role of the last one during therapy with oral NA is still debatable.

Nevertheless, studies like ours, that shed light on the response of CHB to different antiviral treatments depending on the genotype, are relevant. This is especially true in the case of relatively unknown genotypes like genotype E, a genotype associated to immune scape mutations [26] and whose epidemiological impact is steadily increasing in the Western world due to migration from Africa. Improving our knowledge on CHB genotype E infection and its response to treatment is critical to issue proper and specific recommendations. In addition, although access to NA in Africa is currently difficult, all evidence gathered is useful with a view to future strategies for the treatment and prevention of this disease in the countries of origin. May our work then be considered a small and humble contribution to HBV infection clinical care research.

As shown in this real practice study, treatment with nucleos(t)ide analogues is safe and effective in sub-Saharan migrants with CHB genotype E infection. However, direct comparison studies seem to be necessary to conclude whether there are significant differences in the response to treatment when compared to other HBV genotypes.

Migration is altering geographical distribution of HBV genotypes around the world making considering the clinical and epidemiological implications of less known HBV genotypes, such as genotype E, critical in order to provide proper tailored care.

In our setting, where health care and antiviral drugs are cost-free and available with no barriers, high rates of adherence to treatment can be achieved. But these results could also be transferable to low- and middle-income African populations if therapy with such drugs were to be generally available in the future, contributing to research into a neglected disease that affects a large part of the population living in the poorest regions of the world.